Can Brain Imaging Differentiate Between Unipolar and Bipolar Depression?

Major depressive disorder affects an estimated 14.8 million people ages 18 and older, or about 6.7% of the U.S. population.1 There are several types of depression, each of which has some defining symptoms and characteristics. However, people with mental health disorders often have comorbid conditions, creating diagnostic challenges for clinicians. This is especially challenging in people with bipolar disorder, with one in five patients receiving an inaccurate diagnosis. When depression is the most pronounced symptom, manic episodes may be overlooked and only the patient’s depression is treated.

Types of Depression

Major depression (also called unipolar depression): This is characterized by severe symptoms that last for at least two weeks, including being sad or irritable. Depression interferes with the ability to work, sleep, eat and participate in activities that were once enjoyable. Disabling episodes of depression can occur once, twice or several times in a person’s lifetime.

Persistent depressive disorder (also called dysthymia): This type of depression is typically less severe than major depression, however it lasts a long time. To qualify for this classification, symptoms need to be chronic — persisting for a minimum of two years. While this type may not be as disabling as major depression, the symptoms can diminish a person’s ability to fully function and enjoy life. People with persistent depressive disorder may also experience episodes of major depression. When this combination occurs, it is often referred to as double-depression.

Bipolar disorder (formerly called manic depression): Not as common as other types of depressive illnesses, bipolar disorders involve moderate to extreme mood cycles that include at least one episode of mania or hypomania and a varied number of depressive episodes. There are three types of bipolar disorder, with bipolar II being the one with the most dominant depression symptoms, and therefore the form that is most often misdiagnosed.2,3

Neuroimaging 101

The two main types of neuroimaging tests are structural and functional. Structural imaging modalities create a “snapshot” of the brain’s structure, including bone, tissue, blood vessels, tumors, infection, damage and bleeding. Functional imaging reveals the brain’s ever-changing activity and chemistry by measuring the rate of blood flow, chemical activity and electrical impulses during specific tasks. Currently, the use of neuroimaging to detect mental illnesses is in investigational stages, undergoing clinical research studies. However, early findings show the potential future use of neuroimaging including MRI and PET scans for depression and other mental health disorders.4

The Potential of Imaging for Identifying Depression Types

In a small study published in the British Journal of Psychiatry, a research team at the University of Pittsburgh looked for potential biomarkers that could yield a definitive diagnosis of unipolar depression versus bipolar depression. The study of 54 adult women utilized a new, minimally invasive imaging method called arterial spin labeling (ASL). ASL was used to measure blood flow in subdivisions of the study subjects’ brains associated with depression. The researchers achieved an accuracy rate of 81% in identifying which of the subjects had unipolar depression and which had bipolar depression. While this study was limited in size and the findings were preliminary, the researchers were optimistic about the potential of neuroimaging to yield key brain biomarkers for these disorders. While larger studies are warranted, “bipolar brain scan” technology has the potential for yielding an earlier diagnosis than other current clinical methods.5

Additional Research Findings

A two-center cross-sectional study was performed, analyzing 58 depressed patients with bipolar I disorder, 58 age- and sex-matched unipolar depressed patients, and 58 matched healthy controls. According to research findings published in JAMA Psychiatry in November 2014, there were reductions in white matter volume within the cerebellum and hippocampus in individuals with bipolar disorder. This provides strong evidence that structural abnormalities in neural regions that support emotion processing are different in individuals with unipolar depression than in people with bipolar disorder. The authors believe that neuroimaging and multivariate pattern classification techniques hold promise as diagnostic methods for delineating these two major mental health disorders.6